1. Field of the Invention
The present invention relates to a solid-state imaging device and a method for producing the same. More specifically, the present invention relates to a light-shielding film constituting pixels and a method for producing the same.
2. Description of the Background Art
In recent years, a demand for solid-state imaging devices has been increased, and the number of pixels has been increased while the size of a pixel has been increasingly reduced. In general, the pixels of a solid-state imaging device are provided with a light-shielding film in order to prevent light from falling on a portion other than a light-receiving area, and an opening through which light enters the light-receiving area is formed in a portion of the light-shielding film (e.g., Japanese Laid-Open Patent Publication No. 10-284710).
Hereinafter, a conventional solid-state imaging device will be described with reference to FIG. 9. FIG. 9 is a cross-sectional view showing the structure of a relevant portion of a conventional solid-state imaging device. In FIG. 9, a semiconductor substrate 1 is a substrate for forming a solid-state imaging device. A photodiode 2 serving as a sensor portion is formed in the main surface of the semiconductor substrate 1, and generates charges in accordance with the intensity of received light. Charge transfer portions 20 are formed in the main surface of the semiconductor substrate 1 and transport charges that are generated in the photodiode 2. A gate insulating film 3 is formed so as to cover the semiconductor substrate 1. Gate electrodes 4 are provided adjacent to each photodiode 2 via the gate insulating film 3 on the semiconductor substrate 1 and serve as a switch for moving charges generated in the photodiode 2 to the charge transfer portions 20. An interlayer insulating film 5 is formed so as to cover the gate insulating film 3 and the gate electrodes 4. A light-shielding film 10e is formed so as to cover the gate electrodes 4 to prevent light from falling on the gate electrodes 4.
A tungsten film having excellent light-shielding properties is used for the light-shielding film 10e, and in this example, a multilayered film in which a tungsten-sputtered film 11 that is formed by sputtering and a tungsten CVD film 12 that is formed by CVD (chemical vapor deposition) are laminated is used. In general, the tungsten CVD film 12 has a weak adherence with the interlayer insulating film 5 formed of silicon oxide, so that the tungsten-sputtered film 11 is provided as an adhesive layer between the interlayer insulating film 5 and the tungsten CVD film 12. An opening portion 6 is formed by removing the light-shielding film 10e positioned on the photodiode 2 to allow the photodiode 2 to receive light.
FIGS. 10A to 10E are cross-sectional views in each stage in the process of producing the light-shielding of the solid-state imaging device shown in FIG. 9. Hereinafter, a method for producing the light-shielding film 10e will be described with reference to FIGS. 10A to 10E. FIG. 10A shows a state in which the tungsten-sputtered film 11 is formed as a first film constituting the light-shielding film 10e on the semiconductor substrate 1. First, the photodiode 2 and the charge transfer portions 20 are formed in the main surface of the semiconductor substrate 1 by ion implantation or other methods. The gate insulating film 3 is deposited on the surface of the semiconductor substrate 1 by thermal oxidation or the CVD method. When the deposition of the gate insulating film 3 is completed, a necessary pattern (not shown) is formed by depositing a polysilicon film by the CVD method and performing photolithograph and dry-etching or the like so that the gate electrodes 4 are formed. Then, the interlayer insulating film 5 made of silicon oxide is deposited by oxidation/CVD method so as to cover the gate electrodes 4 and the gate insulating film 3. On the surface of the thus constituted substrate, the tungsten-sputtered film 11 having a thickness of 50 nm is formed as a first film constituting the light-shielding film by sputtering.
FIG. 10B shows a state in which the tungsten CVD film 12 is formed as a second film constituting the light-shielding film. First, after the tungsten-sputtered film 11 is deposited, the tungsten CVD film 12 having a thickness of 150 nm is deposited thereon by the CVD method. More specifically, using WF6 (tungsten hexafluoride) and SiH4 (silane gas) as reactant gas, a tungsten nucleation layer having a thickness of 50 nm is formed by supplying WF6 at 20 sccm and SiH4 at 10 sccm and controlling the chamber to be 30 Torr. Then, the tungsten CVD film 12 having a thickness of 150 nm is formed by supplying WF6 at 95 sccm and H2 (hydrogen gas) at 2000 sccm and controlling the chamber to be 90 Torr.
FIG. 10C shows a state in which a resist pattern 7 is formed in order to obtain a light-shielding film having a desired shape. First, after the tungsten CVD film 12 is deposited, a surfactant is applied thereon. As the surfactant, for example, hexamethyldisilazane (HMDS) [chemical formula: (CH3)3Si—NH—Si(CH3)3] is used. Then, after a HMDS treatment is performed, a resist is applied so that a resist film is formed. This resist film is exposed to light and developed, so that a resist pattern 7 that is patterned so as to form an opening portion 6 above the photodiode 2 is formed.
FIG. 10D shows a state in which the first and the second films constituting the light-shielding film 10e are patterned. The tungsten CVD film 12 and the tungsten-sputtered film 11 are dry-etched, using the resist pattern 7 as a mask. Thus, the tungsten CVD film 12 and the tungsten-sputtered film 11 corresponding to the opening portion 6 are removed.
Finally, the resist pattern 7 is removed, so that the patterned light-shielding film 10e can be obtained, as shown in FIG. 10E.
In recent years, with miniaturization of pixels, the pattern size of the light-shielding film 10e is being reduced. With this, peeling of the resist pattern 7 at the time of patterning the light-shielding film 10e has become a large problem.
The resist film constituting the resist pattern 7 inherently has a poor adherence with the tungsten CVD film 12. Therefore, the adherence between the tungsten CVD film 12 and the resist pattern 7 is increased by treating the surface of the tungsten CVD film 12 with a surfactant such as HMDS as described above. However, when the size of pixels is reduced, the area to which the surfactant is applied is also reduced, and therefore, after light exposure and development, the resist pattern 7 is easily peeled from the tungsten CVD film 12. When the tungsten-sputtered film 11 and the tungsten CVD film 12 are subjected to an etching treatment, using the peeled resist pattern 7 as a mask, then the light-shielding film 10e having a desired pattern cannot be obtained, and the yield is deteriorated.